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21Īlthough papain solutions have good temperature stability, the solution stability is pH dependent. Activation/stabilizing agents include EDTA, cysteine, and dimercaptopropanol. Immediately prior to use, the enzyme is typically diluted in buffer containing ~5 mM L-cysteine. in staining tissue for electron microscopy. Fab fragments allow more exact localization of the target antigen, i.e. These fragments may also be desirable for staining cell preparations in the presence of plasma, because they are not able to bind complement, which could lyse the cells. Use of Fab fragments ensures that the antibodies are binding to the antigen and not to Fc receptors. In tissues such as lymph nodes or spleen, or in peripheral blood preparations, cells with Fc receptors (macrophages, monocytes, B lymphocytes, and natural killer cells) are present which can bind the Fc region of intact antibodies, causing background staining in areas that do not contain the target antigen.Lane, ed., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1988. Protocols for antibody digestion and purification of antibody fragments can be found in Antibodies: A Laboratory Manual, E. The fragments can be purified by gel filtration, ion exchange, or affinity chromatography. This generates two separate monovalent (containing a single antibody binding site) Fab fragments and an intact Fc fragment.

14 It cleaves above the hinge region containing the disulfide bonds that join the heavy chains, but below the site of the disulfide bond between the light chain and heavy chain. Papain cleaves antibodies into two Fab fragments, which recognize the antigen specifically with their variable region, and one Fc fragment.IgM may also be digested with papain resulting in high yields of homogeneous Fab preparations. Papain is used routinely for the preparation of Fab fragments from IgG. In these cases it is preferable to use only the antigen binding (Fab) portion of an antibody. Fab and F(ab') 2 antibody fragments are used in assay systems where the presence of the Fc region may cause problems.Papain has also been used in the enzymatic synthesis of amino acids, peptides, and other molecules.

Papain has also been shown to be useful in platelet serology.

Papain is used in red cell serology to modify the red cell surface to enhance or destroy the reactivity of many red cell antigens as an adjunct to grouping, antibody screening, or antibody identification procedures.

Limited papain digestion has proven useful for structural studies of enzymes and other proteins.

3,4 Papain was found to significantly increase the yield of viable smooth muscle cells while not affecting cell sensitivity to stimulants. P4762 ) has been used for the isolation of smooth muscle cells. For example, papain has been used to isolate viable, morphologically intact, cortical neurons from postnatal rats.

Papain is commonly used in cell isolation procedures where it has proven more efficient and less destructive than other proteases on certain tissues.

It does not accept Val at the P1' position. Papain exhibits a preference for an amino acid bearing a large hydrophobic side chain at the P2 position. Papain exhibits broad specificity, cleaving peptide bonds of basic amino acids, leucine, or glycine. Papain will digest most protein substrates more extensively than the pancreatic proteases.